Question

我是初学Android开发人员，现在我正面临着使用谷歌凌空进行http调用的大问题。我创建了自己的库来处理所有REST API请求，我必须将响应返回给ACTIVITY，但是调用是异步的，当我调用return时，它还没有到达。这是lib：

public class RestServices implements IRestServices {
Object responseFromServer = null;
public Object getJsonResponseObjectByAttributes(String... attributes) {
        RequestQueue queue = VolleyProvider.getQueue(ConnectionConstants.context);
        String finalUri = makeRequestUri(attributes);
        JsonObjectRequest jsonRequest = new JsonObjectRequest(
                Request.Method.GET, finalUri, null, new Response.Listener<JSONObject>() {

                    public void onResponse(JSONObject response) {


                    }
                }, new Response.ErrorListener() {

                    public void onErrorResponse(VolleyError error) {
                        // TODO Auto-generated method stub

                    }
                });

        jsonRequest.setTag(ConnectionConstants.TAG);
        queue.add(jsonRequest);

return responseFromServer;
}

以下是我称之为服务的地方：

public class MainViewModel implements IMainViewModel {

    @Inject IRestServices restServices;

    // Define our server URL
    public static final String SERVER_URL = "API_Url";

    public String getServerResponse() {
        Object jsonResponse = restServices.getJsonArrayResponseObjectByAttributes("");
        User user = (User) jsonResponse;
        return user.toString();
    }

    public void InitializeViewModel(Context context) {
        restServices.InitializeService(SERVER_URL, context);    
    }

}

我也在使用Roboguice进行IoC。提前谢谢。

Answer 1

您需要将结果分配给变量并实施等待直到收到结果：

public class RestServices implements IRestServices {
    private Object responseFromServer = null;

    public void getJsonResponseObjectByAttributes(String... attributes) {
        RequestQueue queue = VolleyProvider.getQueue(ConnectionConstants.context);
        String finalUri = makeRequestUri(attributes);
        JsonObjectRequest jsonRequest = new JsonObjectRequest(
            Request.Method.GET, finalUri, null, new Response.Listener<JSONObject>() {
                public void onResponse(JSONObject response) {
                    //add this line to update the result
                    responseFromServer = response;
                }
            }, new Response.ErrorListener() {
                public void onErrorResponse(VolleyError error) {
                    // TODO implement Error handling
                }
            });

        jsonRequest.setTag(ConnectionConstants.TAG);
        queue.add(jsonRequest);
    }
    //added getter for result
    public Object getResponseFromServer(){
        return responseFromServer;
    }
}

这是一个忙碌的等待（因为它更容易显示它应该如何工作）并消耗大量的CPU使用。你应该用阻塞等待替换它（读取线程方法等待，通知和产生以及像信号量一样的锁定）。

public String getServerResponse() {
    restServices.getJsonArrayResponseObjectByAttributes("");
    while(restServices.getResponseFromServer() == null){
        //busy waiting to get sure the result is != null after this loop;
        Thread.sleep(10);//add catch
    }
    Object jsonResponse = restServices.getResponseFromServer();
    User user = (User) jsonResponse;
    return user.toString();
}

Answer 2

如果我理解正确，你打算在打电话后不从你的方法返回，而是在结果出现之后。下面是一个如何执行此操作的示例，该示例的关键是使用future，然后执行future.get（），此代码将不会继续执行，直到Web服务有响应。

//fill params
 JSONObject params = new JSONObject();
 params.put("username", username);
 params.put("password", password);

 //create future request object
 RequestFuture<JSONObject> future = RequestFuture.newFuture();
 //create JsonObjectRequest
 JsonObjectRequest jsObjRequest = new JsonObjectRequest(Request.Method.POST, URL, params, future, future);
 //add request to volley
 MyVolley.getRequestQueue().add(jsObjRequest);
 try {
            JSONObject response = future.get();// this is where the process will 
                                                //wait until a result comes back
            } catch (Exception e) {
            e.printStackTrace();
     }
     return response;

Android Volley：自己的REST Lib

2 个答案: